45Ca2+ uptake by dispersed pancreatic islet cells: Effects ofd-glucose and the calcium probe,chlorotetracycline

Uptake of⁴⁵Ca²⁺ was studied in dispersed pancreatic islet cells from non-inbredob/ob-mice. Like whole islets the dispersed cells responded to 20 mMd-glucose with a markedly increased⁴⁵Ca²⁺-labeling of both the lanthanum-nondisplaceable and the lanthanum-displaceable calcium pools. The pronounced effect ofd-glucose could not be reproduced with 3-O-methyl-d-glucose,l-glucose,d-mannose,l-leucine, ord-leucine; however,⁴⁵Ca²⁺ uptake was greater in the presence ofl-leucine as compared withd-leucine.⁴⁵Ca²⁺ uptake by dispersed cells or whole islets was stimulated severalfold by 100 M or more chlorotetracycline. At the concentration of only 10 M, chlorotetracycline had no effect on whole islets and partially inhibited⁴⁵Ca²⁺ uptake by the dispersed cells. The ability ofd-glucose to stimulate⁴⁵Ca²⁺ uptake by islets or dispersed cells remained in the presence of 10 M chlorotetracyline. Islet cell suspensions apparently represent a valid model for studying how Ca²⁺ interacts with the cells. However, when using chlorotetracycline as fluorescent Ca²⁺ probe, attention must be paid to its potential ionophoric activity. At only 10 M, the drug seems to monitor a peripheral pool of Ca²⁺, some of which may reside in normal transport channels.